Doolittle on the Steam Engine. 105 
motion to the machine, we have force expended in describ- 
ing the are B‘AB=force employed in describing the arc 
B, A’, B’—Therefore, besides the continual variation in 
the intensity of the force utilized, we find that a much greater 
portion of the force required fora revolution is spent in de- 
scribing the semicircle f. A. g. than in describing the semi- 
circle g. A’. f—and we must not forget that this is the por- 
tion of the revolution where the effect is greatest in propor- 
tion to the force employed ; therefore if the motion of the 
piston in the cylinder be uniform, the motion of the cylin- 
der in its revolutions must be irregular and vice versa. 
Add to this, that with the velocity which Mr. Sullivan 
proposes giving to this machine, the influence of the centri- 
fugal force ought to be taken into consideration—this force 
also not only varies with the dimensions of the machine and 
the weight of the piston, but is different at every instant, in 
the same machine, increasing as the piston recedes from the 
centre, and diminishing as it approaches; augmenting the 
effect of the machine in the first instance and diminishing 
it in the latter ; more force is therefore developed in going 
from A through B to A’, than in going from A’ through B’ to 
A=another cause of irregularity in its movements, to coun- 
teract these effects the machine should be made very heavy, 
to serve as a fly wheel. 
Ihave hitherto considered this engine without reference 
to its friction; this, in certain points of its revolution, must 
be immensely greater than in the old engine, as will appear 
evident to the most superficial observer, on a simple inspec- 
tion of its construction. 
These are some of the imperfections which this engine 
possesses in addition to all-those of the common one, and 1 
can discover nothing in its favour but novelty. 
There is no doubt but it will turn, if it be not too much 
loaded, and its movements will probably produce an agree- 
able effect, but I do not apprehend that Oliver Evans has 
any thing to fear from its rivality. 
You are at liberty to make what use you please of this 
communication. 
I am, sir, very respectfully, 
Your obedt. servt. 
1. DOOLITTLE. 
Vou. .....No. 1. 14 
